In 2011, 150,000 people within 20 kilometres of the Fukushima nuclear plant needed evacuation. Since the meltdown in the Japanese coastal city, Germany, Switzerland and Sweden have all decided to extend evacuation zones around their nuclear power plants from 10 to 20 kilometres.

How smoothly emergency evacuation would proceed is uncertain, since traffic plans remain on the drawing board. Also unknown is how evacuees would be supported in a displacement that could last a year or longer. It doesn’t help public’s confidence in emergency plans that the cabinet committee charged with overseeing provincial emergency management hasn’t met in eight years years.

In Japan, the evacuation itself, along with living conditions in evacuation centres, have been blamed for killing at least 1,600 people two years after the disaster. That is more than died in the earthquake and tsunami that led to nuclear meltdown and the evacuation in the first place.

Fifteen-metre waves aren’t likely to smash the shores of Lake Ontario anytime soon, but it wouldn’t take a tsunami to cause a breakdown in one or more of Ontario’s nuclear reactors. Anything from a tornado to a mechanical failure could set the stage.

Pickering Nuclear Generating Station’s reactors are among the oldest in the world. OPG is currently seeking permission to keep the plant pumping until 2024, pushing reactors years past their design lifetimes and, critics say, increasing the risk of a serious accident.

Sitting 30 kilometres from the heart of Toronto, just over two million people live within Pickering’s nuclear fallout zone, more than any other nuclear plant in North America. The human impact of a severe accident there could dwarf Fukushima’s, where about 174,000 people remain displaced and remediation is expected to continue for 40 years at a cost of USD $188 billion.

“The problem with nuclear power is that it’s alright until it isn’t,” says Gordon Edwards, president of the Canadian Coalition for Nuclear Responsibility. At Fukushima, it was a power outage, not a defect in the reactor itself, that caused by the tsunami that prevented the cooling of the reactor cores, which led to meltdown.

Though the likelihood of a full-blown disaster is remote, Pickering’s six operating reactors have a history of accidents involving releases of radioactive substances into the air and water of Lake Ontario. A severe incident would compromise public health and leave large parts of the region around Toronto uninhabitable.

All nuclear reactor designs have their flaws. CANDU’s system of hundreds of fuel and cooling tubes is complex. Tubes weaken with years of exposure to the heat, pressure, corrosion and radiation inside a reactor core and are expensive to monitor and replace. A single break could trigger an accident, but only a sampling of these tubes are tested and inspected periodically.

“There’s this mentality within Canada that [CANDUs are] safer. I would say, they’re just lucky,” says Arnie Gundersen, a nuclear engineer and former nuclear industry executive turned whistle-blower, who notes that the three major meltdowns of the last 35 years – Three Mile Island, Chernobyl and Fukushima – involved reactors with distinct designs.

If the vacuum building were to fail, Toronto is toast, says Gunderson.

“There is no way to get out quick enough and there’s probably no place to go either,” he says.

Even if the wind cooperated, with the lake to the south and the plant to the east, an evacuation could put millions on highways heading just west or north.

Ted Gruetzner, vice-president of corporate relations and communications at OPG, touts the robustness of Pickering’s reactors.

Gruetzner says a multi-unit accident would not overwhelm the vacuum building. If that were the case, Pickering would not be allowed to operate.

He says the company has taken steps to make “our safe plants even safer” by adding devices that prevent explosive hydrogen build-up inside reactors after an accident. OPG has also added extra generators, backup water supplies and more water barriers to mitigate against the kind of flooding and power outage that caused Fukushima.

But critics say Pickering is still missing filtered reactor vents, which release pressure from the core while keeping a lid on radiation. The vents have been installed on other OPG reactors but with Pickering scheduled to close in 2024, their installtion was judged not to be cost effective.

The wind pushed more than 80 per cent of Fukushima’s initial radiation release into the Pacific Ocean. Since then, more than 760,000 tonnes of radioactive water has leaked from the hobbled plant. It continues to leak.

The same circumstances would spell tragedy here, as Lake Ontario is the source of drinking water for 9 million people. Likely pollutants would include tritium, radioactive iodine, which harms the thyroid, cesium, which attacks heart muscles, and strontium, which causes leukemia.

Even though an accident could poison the water of downstream communities as far away as Montreal, a provincial study promised in 2013 to look at the risks of a spill – and how to provide alternate drinking water for millions – has yet to materialize.

OPG’s Gruetzner insists Pickering is designed to keep any leaks within the plant.

At Fukushima, over a million tonnes of radioactive water is currently being stored on-site in 900 massive tanks. Each day brings another 150 tonnes of tainted water, a by-product of the effort to keep the melted-down reactor cores cool. The mostly decontaminated water contains tritium but may nevertheless soon be released into the Pacific.

Asked whether there is any chance Lake Ontario could be poisoned in a severe nuclear accident, Gruetzner offers a stock response. “We have the systems in place, the operations in place, that keep the environment and the people of Pickering and Toronto safe.”

There are too many unknowns to be so certain, Gundersen says.

“I have just seen too many things fail in ways that engineers never anticipated. This is a technology that can turn on you overnight. It’s 40 good years and one bad day. And the one bad day wipes out everything that went before it.”